The present invention relates to systems for utilizing telephone networks to provide additional functions, beyond those of traditional telephone service involving conversations between subscribers. More particularly, the invention relates to such systems in which the network is additionally used to monitor the conditions of one or more instrumentalities, located at the subscribers' premises.
U.S. patent application Ser. No. 327,486, filed Dec. 4, 1981, assigned to the same Assignee as the present application and hereby incorporated by reference, is directed to a system which utilizes a telephone network to "poll" one or more instrumentalities, such as fire alarms and burglar alarms, located at the premises of the telephone subscribers to determine the status of any particular instrumentality. Interrogation signals are transmitted via the telephone lines to terminals, referred to as subscriber terminal units or STU's in application Ser. No. 327,486, and the nature of the response indicates the status of the monitored instrumentality. If an alarm condition is sensed, an appropriate agency, such as the local fire department or police precinct, is notified. The system described in application Ser. No. 327,486 is but one of many such systems which have been proposed previously.
The polling unit, identified as the scanner in application Ser. No. 327,486, is the source of the interrogation signals which are transmitted to the subscriber terminals to determine the status of the instrumentalities being monitored. The polling unit also provides the indications of alarm conditions. In addition, the polling unit performs other complex functions, such as the prioritized selection of particular subscriber terminals to be interrogated, the assignment of components which generate a sequence of interrogations and the frequency of interrogations. In performing all of these functions, the polling unit develops a history of the responses from the subscriber terminals by storing the responses.
The polling unit should be arranged not only to identify alarm conditions of the monitored instrumentalities, but it also should detect breakdowns and malfunctions within itself. Preferably, a defective or malfunctioning component or portion of the polling unit is automatically taken out of the system and a fully operational replacement is automatically substituted. In this manner the polling unit operates continuously with the result that the subscribers receive uninterrupted, effective surveillance of the instrumentalities at their premises.
The replacement of malfunctioning components within the polling unit preferably is conducted on a selective basis rather than by full-scale substitution of one entire polling unit for another. By substituting selectively, more malfunctions can be overcome with only one back-up unit than when the entire back-up unit is substituted on the occurrence of a single malfunction.